1. Field of the Invention
This invention relates to improved surfactants useful in the recovery of oil, and to methods employing the same. More particularly, it relates to hydrolytically stable forms of alkylaromatic sulfonates which may be used with steam in enhancing recovery of subterranean oil.
2. Description of the Prior Art
The use of aqueous flooding techniques, with or without the addition of various reagents such as surfactants, water thickeners and the like to recover crude oil left behind in formations after the "primary" oil has been withdrawn is well established in the art. These displacement methods have been improved by the aforesaid surfactants and the like in both secondary and tertiary processes, as where a formation has already been waterflooded at least once.
Representative of the prior art compositions and methods described above are those taught in U.S. Pat. Nos. 3,348,611 to Reisburg; 3,885,626 to Gale et al; 3,901,317 to Plummer et al; 3,994,342 to Healy et al; and 4,295,980 to Motz, all of which teach aqueous flooding techniques with at least one surfactant, and in some cases, with viscosity modifiers, co-surfactants or the like. Amongst the more preferred surfactants employed have been the alkyl aryl sulfonates, and particularly the dialkyl aryl sulfonates such as those derived from the alkylation of toluene, ethylbenzene, and the like.
In addition to the aforedescribed aqueous flooding techniques, the art has also employed steam, principally for tertiary oil recovery, utilizing the effect of heat to obtain heavy oil from the formations in which it is found. See, for example, U.S. Pat. Nos. 3,357,487 and 3,994,345.
The mechanism and effects of surfactants under these high temperatures and diverse formation conditions remain unclear, and thus make it impossible to predict from a knowledge of the effects of aqueous surfactant systems which surfactants, if any, can advantageously be employed in these steam recovery conditions. However, it is known that over a period of time these sulfonated surfactants do become deactivated as a result of the loss of their sulfonate groups because of the high temperatures and other operating conditions of the steam recovery methods. It is, therefore, an object of this invention to provide alkylaromatic surfactants, and particularly dialkylaromatic sulfonates, which are more stable under the operating conditions of steam recovery methods than those of the prior art.
These and further objects and advantages of the methods of the present invention will become apparent in the course of the following detailed description thereof.